1. Field of the Invention
The present invention relates to a disk array device and a maintenance method for the disk array device.
2. Description of the Related Art
A disk array device is established, for example, by arranging a large number of disk drives in array and on the basis of RAID (Redundant Array of Independent Inexpensive Disks). A logical volume, which is a logical storage area, is formed on a physical storage area provided in each disk device. A host computer can read and write desired data by issuing a writing command or a reading command of a predetermined format to the disk array device.
Various preventive measures are applied to the disk array device in order to prevent loss or the like of data stored in the disk drives. One of the preventive measures is adoption of a RAID configuration. For example, the disk array device adopts a redundant storage configuration, which is known as RAID 1 to 6 or the like, whereby likelihood of data loss is reduced.
Moreover, duplexing of a physical configuration is also performed in the disk array device. For example, in the disk array device, duplexing is realized by providing plural principal parts such as host interface circuits, which perform data communication with a host computer, and subordinate interface circuits, which perform data communication with the respective disk drives. In addition, there are also provided plural paths for connecting the principal parts, respectively, plural power supplies for supplying power to the respective principal parts, and the like.
In addition, the conventional disk array device includes shared memories and cache memories such that control information is stored in the shared memories and data is stored in the cache memories (JP-A-2000-339101). In the conventional technique, both the shared memories and the cache memories are mounted in one memory package. Further, in order to supplement a cache capacity, cache memories are also mounted in a selector package.
User data, which has been requested by a host apparatus to be written in the disk drives but has not been written in the disk drives yet, is required to be stored in plural cache memories to be duplexed. This is for performing data guarantee. In addition, control information for controlling an operation or the like of the disk array device is also required to be duplexed from the viewpoint of securing redundancy. By duplexing the control information, even in the case in which one piece of control information becomes unavailable due to occurrence of a failure or the like, requests for reading and writing from the host apparatus can be processed on the basis of the other piece of control information.
However, with a configuration in which control memories storing control information and cache memories storing user data are provided in identical packages, in the case in which a failure occurs in a control memory or a cache memory, responsiveness declines during a period until maintenance and replacement work of an entire package, in which the failure has occurred, is completed.
In the case in which a writing request is received form the host apparatus in a normal state in which a failure has not occurred in both the packages, it is possible to inform the host apparatus of completion of writing at the point when data is stored in the cache memories. The data requested to be written is duplexed in the cache memories and guaranteed. Thus, no inconvenience is caused even if the host apparatus is informed of completion of writing before writing the data in the disk drives.
On the other hand, in the case in which entire one package is subjected to blocking processing, only the control memories and the cache memories mounted to the other package, which is operating normally, can be used. Therefore, in this case, since data cannot be guaranteed by duplexing, it is impossible to inform the host apparatus of completion of writing at the point when data requested to be written is stored in the single cache memory. Thus, in the case in which one of the packages is unavailable, the host apparatus is informed of completion of writing after the data requested to be written is written in the disk drives. This response operation is called, for example, a “pseudo through operation”.
Even at the time of the pseudo through operation, the disk array device can continue operation normally. However, since response to the host apparatus is delayed, performance of the disk array device falls. The pseudo through operation continues throughout a period from the time when the package, in which a failure has occurred, is replaced until the time when necessary work is completed. Therefore, the pseudo through operation is performed over an entire period required for maintenance and recovery, and responsiveness of the disk array device falls.